In general an absolute and relative accuracy of power adjustment can be required for any transmit device. This accuracy requirement shall be achievable with minor effort (e.g. calibration) due to time and cost concerns.
In conventional systems, the relationship between output power and a control parameter for adjusting the power is nonlinear. A disadvantage is a complex (time consuming) calibration process. Furthermore the characteristic of the output power is mostly strongly dependent on process and temperature variations unless big effort is spent on the design.